[TUT] Android Gradle App with JVM JUnit tests

This tutorial will show you the skeleton of an Android application that uses the Gradle build system and runs JUnit tests on java classes.

If your here and reading this, I assume you already know Android code runs on Dalvik and the SDK’s used when developing on a computer are stubs. (Hence the Stub! exception when you try and run JVM tests on an Android class).

The concept of this project is to separate your code into two modules the first is your Android application module and this has a dependency on the Android SDK. The second is a plain java module that has no dependency on Android only on Java, the catch being your first module has a dependency on the second. Therefore the Android code can see the java code but the java code cannot see Android! This is a good thing and allows you to write your applications domain login in pure Java and of course let’s you write JVM JUnit tests that run super fast for instant feedback.

Android studio has a wizard for creating new modules, you’ll want to pick the Java only type for your “core” module.

Once you have done this, your settings.gradle file will be updated showing the new module. This lets gradle know the module exists.

include ':app', ':core'

The second thing you need to do is add the dependency from the app (Android module) to the core (Java module). This is done in your app modules build.gradle:

dependencies {
    compile project(':core')
}

Lastly you’ll want to set up your core java module for testing. We are now in standard java world. So tests sit in /test/java and your code in /main/java.

Now that you have a pure java module, you can leverage the whole java ecosystem and can add static code analyses like checkstyle, findbugs or PMD & also get code coverage of your java module with jacoco or emma. These can be added as simple plugins with minimum setup.

Now add any dependencies you want to code java module build.gradle:

apply plugin: 'java'

dependencies {
    testCompile 'junit:junit:4.+'
}

And write your tests:

public class MyJvmClass {

    public String getHelloWorld() {
        return "Hello World";
    }
}

public class MyJvmClassTest {

    @Test
    public void testHelloWorld() throws Exception {
        MyJvmClass myJvmClass = new MyJvmClass();

        String text = myJvmClass.getHelloWorld();

        assertEquals(text, "Hello World");
    }
}

Thats it! To run your tests you can use one of these:

• ./gradlew test
• ./gradlew check
• ./gradlew build

test just runs your tests, check would run tests plus checkstyle etc, and build compiles everything & checks & tests

Source Code

The example project is available on GitHub Check it out here